Nanoscale Origin of Conductance Dips in Point-Contact Spectra of Superconductors

In this contribution, we summarize current progress in identifying the origin of above-gap ‘anomalous’ features regularly observed in point-contact spectra of superconducting materials. It is shown that their origin can be associated with a nanoscale degraded coating whose contact with the superconducting bulk is imperfect. To verify this hypothesis, we have performed control measurements of differential conductance – versus – voltage bias dependences for point contacts based on Pb, thoroughly studied superconductor with a single energy gap, and a novel two-band superconducting MgB 2 compound. Calculated characteristics well describe experimental findings for these two fundamentally different materials.